1. Field of the Invention
The present invention relates to a thermally assisted magnetic recording medium for magnetically recording and reproducing information on a recording region by a temperature rise obtained by means of a heat source.
2. Description of the Related Art
As one of high density magnetic recording and reproducing techniques, for example, Japanese Unexamined Patent Publication No. Hei 4(1992)-176034 has disclosed a magnetic recording medium made of an n-type ferrimagnetic substance having a compensation point at almost a room temperature and a thermally assisted magnetic recording and reproducing method using a laser beam which utilizes the same magnetic recording medium. In such a thermally assisted magnetic recording method, information is recorded by an external magnetic field (a recording magnetic head) in a state where a temperature in a recording region of the medium is locally raised by a laser beam, thereby sufficiently lowering holding force. For reproduction, a temperature in a reproducing region is locally raised by the laser beam to increase the strength of residual magnetization, thereby reading information by means of a reproducing head. This method is characterized in that a recording track width can be decreased and a cross talk can be reduced by using the laser beam as a heat source.
The magnetic recording medium which has conventionally been proposed by the above-mentioned thermally assisted method consists of a glass substrate, a magnetic film, a protective film and a lubricating film. An amorphous carbon film is used as the protective film. In recent years, further enhancement in recording density has been required. For this reason, it is necessary to reduce a magnetic spacing between the magnetic head and the magnetic film. As one of measures, it is considered to reduce the thickness of the protective film. However, if the thickness of the amorphous carbon film is 20 nm or less, a problem arises in that peeling and breakdown of the protective film progress by the abrasion of a head and a disc. In a field of a hard disk which is also a magnetic recording medium, there have been proposed as a new protective film a DLC (Diamond Like Carbon) film (Japanese Unexamined Patent Publication No. Sho 60(1985)-155668) and a carbon nitride film (Japanese Unexamined Patent Publication No. Sho 60(1985)-253021) which are thin but are excellent in hardness and abrasion resistance.
In the magnetic recording medium adopting the thermal assistance, a magnetic alloy film made of three metals of Tb, Fe and Co is used. However, it is problematic in that a magnetic recording medium using such a rare earth-transition metal is generally oxidized easily and less reliable. The reason is that Tb which is a rare earth element is easily oxidized. In particular, in the thermally assisted recording method performed at high temperatures, if the protective film is made of amorphous carbon or DLC, there is a problem in that oxygen in the air diffuses and proceeds into a magnetic film through the protective film, thereby changing the magnetic characteristics of the magnetic film.
Further, in the thermally assisted recording method, it is necessary to take the optical characteristics of a magnetic recording medium into consideration in order to irradiate the medium with laser beam. More specifically, required is the characteristic of suppressing the reflection of the laser beam as much as possible by a protective film, if any, formed on a laser-irradiation side and adsorbing the incident laser beam effectively. In the medium using a DLC film and a carbon nitride film which have been proposed as a protective film for a conventional hard disk, these aspects have been rarely taken into consideration. Therefore it might have a sufficient possibility that an absorption efficiency of the laser beam is not optimum when the laser beam is irradiated.
The present invention provides a thermally assisted magnetic recording medium comprising a recording region for recording information including a recording layer and a carbon nitride film provided on a side from which light is incident with respect to the recording layer, the recording region being locally heated using light as a heat source for magnetically recording and reproducing information.
According to the present invention, it is possible to prevent oxidation of the recording layer and efficiently convert the incident light into heat, thereby reducing an optical power necessary for recording and reproduction.